1. Technical Field
The present invention relates to a receiver and a failure detection method for a receiver. For example, the present invention relates to a receiver related to optical communication and a failure detection method for such a receiver.
2. Background Art
As the Internet traffic has increased, it has been desired to increase the capacity of trunk transmission systems even further. As a technology for increasing the capacity even further, the digital coherent transmission technology is attracting attention. On the receiving side in the digital coherent transmission technology, a receiver equipped with a coherent light receiving unit is used.
The coherent light receiving unit makes an input optical signal interfere with local oscillation light and thereby separates an in-phase optical signal (I-component) from a quadrature phase optical signal (Q-component). Then, the separated optical signal is converted into an electric signal and an analog signal is thereby generated. After that, the analog signal is converted into a digital signal. Further, digital signal processing is performed on the digital signal in a DSP (Digital Signal Processor), so that desired data is demodulated from the digital signal.
An optical receiver, i.e., a receiver used in such a digital coherent transmission technology has been disclosed (Japanese Unexamined Patent Application Publication No. 2010-245772). This optical receiver has a configuration for adjusting the intensity ratio between the optical signal and the local oscillation light in order to improve the reception signal quality when digital coherent communication is performed.
However, the inventors have found out that there are following problems in the receiver like the one described above. There is a case in which when an optical signal is being output from a transmitter, no proper digital signal is output from the receiver due to an occurrence of a failure. In general, the receiver does not have any means for checking whether or not the optical signal is being properly input to the built-in coherent light receiving unit. Therefore, it is impossible to determine whether the failure is caused because no optical signal is being input to the coherent light receiving unit or the receiver itself has broken down. Further, when the failure is caused because the receiver itself has broken down, it is very difficult to determine the aspect of the failure such as the place in the receiver at which the failure has occurred.